Objectives -First, to measure the thermodynamic properties (particularly the activity but also the partial molal heat effects if possible) of representative solutions of permanent gases (such as CH4, C2H6 ..., CO, CO2, and others) in water and heavy water over the approximate pressure range 1 to 1000 torr and temperature range 0 to 100 degrees cantigrade. Also, to continue our measurements now in progress on the thermodynamic properties of other selected solutes in water and heavy water over the same temperature range, and from approximately 1 m to near saturation. Second, to interpret the data from part 1 within the framework of the theory of isotope effects in condensed phases thereby gaining information concerning the structure of the solutions. Methods - The techniques which we propose to use include differential capacitance manometry and differential submarine calorimetry. We have extensive experience with both techniques. The data on the hydrocarbon gases will be useful in adding to the understanding of the phenomenon of hydrophobic bonding. A thorough understanding of solutions of such solutes is an essential prerequisite to understanding the processes which occur in the living cell. The data on the other gaseous solutes will have implications concerning the properties of blood. DTL* 1GM-20022-1*